Telephone system



July- 14, 1942.

P. BAKKER TELEPHONE SYSTEM 2 Smets-sheet `1 Filed April 11, 1940 INVENTOR PIER BAKKER "3 ATTORNEYS :ESG muzi QQ bwl July 14, 1942.

P.Y BAKKER TELEPHONE SYSTEM Filed April 11, 1940 2 Sheets-Sheet 2 INVENTOR PIER BAKKER ATroRNEYs Patented July 14, 1942 'rimirnoNE SYSTEM Pier Bakker, Chicago, lll., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application Api-u 11, .1940, serial No. 329,688

(ci. 17o-1s) v 25 Claims.

'Ihe present invention, relates to telephone systen s and, more particularly, to improvements in automatic telephonesystems of the character of that disclosed and claimed in the copendingapplication of Clarence E. Lomax and Pier Bakker, Serial No. 269,139,` now U. S. Patent No. 2,214,908, granted Sept. 17, 1940, filed April 21, 1939, wherein finder switches are employed to extend con nections between calling lines and associated nu-` merical switches.

It is an object of the present invention to provide in an automatic telephone system, improved distributor apparatus for selecting idle finder switches for the use of calling lines and for controlling the operation of the selected finder switches.

Another object of the invention is to provide in an automatic telephone system, improved distributor apparatus for selectively controlling the operation of the nder switches in two associated groups of finder switchesto find calling lines in twoassociated groups of lines.

The features of the present `invention are il- Alustrated, as beingincorporated in a telephone system provided with an exchange terminating first and second groups of lines and comprising first and second groups of finder-connector links, each link including a finder switch and a connector switch, and first and second distributors respectively associated with the first and second groups of links. These switches are so connected and arranged that each finder switch and each connector switch has access to each line in the system.

In accordance with,` one feature of the inven- 35 tion the telephone system comprises first and second groups oflines, first and second groups of finder switches, each of the finder switches in each of the groups of finder switches having access to each of the lines in each of the groups of 40 lines and being operative to find a calling line accessible thereto, first blocking means normally of nder switches from finding lines in the first group of lines. Also the system comprises a rst distributor operative to assign idle ones of the 540 finder switches in the first group of finder switches in a predetermined order and to initiate operation of an assigned one of the last-mentioned finder switches, means for arresting optioned finder switch when a line is found thereby. means governed when all ofthe nder switches in the iirst group` of finder switches are rendered busyi'or rendering ineffective the second block.

ing means, a second distributor operative to assign idle ones of the nder switches in the second group of finder switches ina predetermined order and to initiate operation of an assigned one of the last-mentioned finder switches, means for arresting operation of and forrendering busy the last-mentioned finder switch` when a line is found thereby, and means governed when all of the finder switches in the second group of finder switches are rendered busylfor rendering ineffective the first blocking means. Finally, this system comprises means governed in response to the presence of a calling line in the first group of lines for operating the first distributor in the event there is an idle finder switch in the first group of finder switches and for operating the second distributor in the event all of the finder switches in the first group of finder switches are busy and governed in response to the presence of a calling line in the second group of lines for operating the second distributor in the event there is an idle finder switch in the second group of nderswitches and for operating the first distributor in the event all of the finder switches in the second group of finder switchesare busy.

In accordance with another feature of the invention each of the distributors i's operative through a cycle to initiate operation of a. preselected finder switch in the associated group of finder switches and then to arrest operation of and to render busy the last-mentioned finder switch when a line is found thereby and finally to select another idle one of the finder switches in the associated group of finder switches.

In accordance with a further feature of the invention the first blocking means comprises a blocking circuit adapted to be completed to prevent the finder switches in the first group of finder switches from finding lines in the second group of lines; and the second blocking means comprises a blocking circuitadapted to be completed to prevent the finder switches in the second group of finder switches from finding -lines in the first group of lines. Furthermore, the first distribu tor comprises means governed when a finder switch in the-first group of finder switches is operating for preparing a point in the first blocking circuit and additional means governed while a finder switch in the first group of finder switches is operating or when there is an idle finder eration of and for rendering busy the last-menswitch in the first group of finder switches for when points are prepared therein in both the first distributor and the second distributor.

Further features of the invention pertain to the particular arrangementof the circuit elements of the system and to the particular con-A nection and arrangement of the elements of the distributors and the links incorporated therein,

whereby the above-outlined and additional operating features are attained. Y

The novel features believed to be characteristic of the invention are set forth Withparticularity in the appended claims. 4TheV invention, -both as to its organization and method of operation, together Vwith further objects and advantages thereof, will best be understood by reference to the following specification takeny in connection with the accompanying drawings in which Figs.v l and 2, taken together, illustrate a telephone system embodying the present invention.

Referring now more particularly to Figs. 1 and 2' of the drawings, the telephone system there illustrated comprises an exchange terminating a plurality of subscriber lines, including the subscriber lines |0| and'230. Also, the exchange comprises a number of finder-connector links, including the links 60 and l0, for setting up connections between the various subscriber lines. More specically, the exchange has an ultimate capacity of 200. lines, these lines being arranged in first and second groups of 100 lines each. Each 0f the links comprises a 200 point finder switch having access to each line in the system and a 200 point connector switch having access to each line in the system.

Furthermore, the links are arranged in first and second groups, each group of links being provided with va distributor individual thereto for assigning idle ones of the links in the group to the use of calling ones of the lines. The number of links included in each group is determined by the amount o f traiiic which the exchange is requiredto handle and usually satisfactory serv- 'ice may be rendered when each of the two groups of links includes ten links.

More particularly, the rst group of links includes the link 60, which comprises the finder switch and the connector switch 2|5, and is provided with the distributor 300; while the second group of links includes the-link 10, which comprises the finder switch 3| 0 and the connector switch 3| I, and is provided with the distributor 3|2. The rst and second groups of lines are respectively associated with the distributors 300 and 3|2; whereby calling lines in the first group of lines are normally assigned for use idle ones of the links in the first group of links, and;calling lines in the second group of lines are normally assigned for use idle ones of the links in the second group of links, thereby rendering it possible to extend simultaneously a call initiated on a line in each of the two groups of lines. Furthermore, the distributors 300 and SI2 are so connected and arranged that acall initiated on a line in the first group of lines is assigned for use an idle link in the second group of links in the event all of the links in the first group of links are busy; and a call initiated on a line in the second group of lines is assigned for use an idle link in the first group of links in the event all of the links in the second group of links are busy.

A subscriber substation is associated with each of the subscriber lines, the subscriber substations A and B being respectively associated with the subscriber lines |0| and 230. Each of the subscriber substations is provided with a telephone instrument, a dial mechanism and a ringer. Also,

'a line circuit is individually associated with each ciated with the subscriber lines |0| and 230.

Preferably, these line circuits are identical, each including a line relay and a cutoii relay, these relays in the line circuit |00 being respectively indicated at R|20 and RI |0.

Preferably. each of the links is connected and arranged in a manner similar t0 that of the link B0 which comprises the finder switch |30 and the connector switch 2|5. The finder switch |30, as best shown in Fig. l, comprises a switching mechanism |40 of the 200 point Strowger type including a bank of xed contact sets arranged in ten vertical levels, each level including upper and lower rows of contact sets, each row of contact sets` including ten circumferentially disposed contact sets, each contact set terminating a line extending thereto; and a row of xed contacts arranged in vertical alignment.

Also, the Strowger mechanism |40 comprises upper and lower wiper sets respectively including the wipers |4|, |42, |43 and |44, |45, |46 carried by a carriage movable in both vertical and rotary directions, the upper and lower wiper sets being respectively associated with the upper and lower rows of contact sets in the bank of xed contact sets; and a control wiper |41 carried by the carriage, the control wiper |4 being associated with the row of fixedv contacts. Also, this Strowger mechanism includes a vertical magnet M|`|0 for moving `the carriage in the vertical direction, a rotary magnet` M|`|| for moving the carriage in a rotary direction, and a release magnet' M|`|2 for releasing the carriage and for causing it to be returned to its normal position. Associated with this Strowger mechanism are two sets of switch springs SI15 and S|`|9 which are actuated by the movement of the carriage in the vertical direction away from its normal position, and a set of switch springs S|14 which is actuated by the movement of the carriage into its eleventh rotary position. Also, it is noted that the upper and lower wiper sets respectively terminate the trunk lines |3| and |35 included in the nder switch |30, which trunk lines are operatively associated with the trunk line ||5 extending between the finder switch |30 and the connector switch 2|5. Also, the finder switch |30 comprises a start relay R|40, two switching relays R|50 and R|60, a

supervisory lamp L|28 and a manually operable y 2.289.890 3 with the iii'stlroup` of `links which comp as best 'shown in Fig. 2, s rotary switch3II `including six-banks ofilxed contacts andsix wip` ers individually associated therewith. the corresponding contacts in each bank terminating the control conductors extending to the respectiveV links in thel first group of.v links, "and the wipers terminating the control conductor extending to the distributori* Also, the rotary switch 30| in` cludes arotary magnet M303 for driving the wipers associated with the contactbanks in a rotary direction. The distributor "300 also comprises a start relayRl, a busy transferrelay R3, a step relay R310, a transfer relay R300, a timing relay R315, first and second test relays R320 and R325, respectively, and a, numberv ofl control relays R350, R300, R300 and R330. Also asso'- obvious path for lpplying ground potential to the s control conductor CI, thereby to cause ground potential to besppliedlby-.wa'y otthe circuit lnetwork IOI-to the start conductorCIIl extendingl into the distributorifassuming that the subscriberline III is included in the iirst groupoi.' subscriber lines. Also, this application ot ground potential toA the control conductor CIII marks, `by way ot the circuit network III and the contacts inthe rows o! contacts in the Strowger mechanisms included in the iinder switchesfthe level wherein the subscriber line III is terminated, `the contact in the row of contacts in the Strowgermechanism |40 included elated with the distributor 300 are a supervisory lamp 1.300 and a busy switch S334.

The distributor 300 is of the preselective type in that an idle link in the first group of links is selected to be assigned to the use of a calling line in the first group of lines prior to the initiation of a call onl the line therein and another idle link in the iirst groupoi links is automatically `selected to be assigned to the useoi the next calling line inthe nrst group of lines as soon as the selected link operates to iind a calling line in the nrst group of lines. Also,

the distributor 300 is so connected and arranged that, when all of the links in the iirst group of links are busy, the start circuit of the distributor 300 is transferred to the distributor 3l! associated with the second group of lines, whereby the distributor 3|!` assigns idle ones oi the links `in thesecond group oi links to the use of calling lines in the firstgroup of lines. Further, the distributors 300 and 3I2 are so connected and arranged that the nnder switch of a link in the nrst group of links is positively preventedfrom ilnding a line in the second group `of lines while the distributor 3l! is operating to the extension of a call from the subscriber substation A to the subscriber substation B. The

call is iirst initiated at the substation A by removing the receiver of the telephone instrument thereat from `its hook, thereby to complete a bridgepath'at the substation A between the lin'e conductors CIU! and CI03 of the subscriber line IOI extending to the substation A. When this bridge path is completed between the line con-l ductors of the subscriber line IOI, a circuit is completed for energizing the winding of the line relay RI20 in the line circuit |00 individually associatedlwith the subscriber linel IOI, which circuit extends from ground, at RAI I2, by way of RAII2,`CI02, the bridge path between the line conductors CI02 and CI03 of the subscriber line IOI, C103, RAIII, and the winding of RI20 to battery. When energized overthe above- Vtraced circuit the line relay R|20 operates to complete, at RAI22 and RCI23, an obvious path 1 for applying ground potential to the control conductor CI of the subscriber line IOI, thereby to mark the subscriber line I 0I as busy to the connector switches having access thereto. Also, v

the line relay RI completes, at RAI25, an

in the finder switch being indicatedrat` III. Also, upon operating, the line relay Rin completes, at RAIZI, a path tor applying battery potential to the control conductor CIM of the subv scriber line III, thereby to mark the rotary position of the contact sets in the contact banks of the Strowger mechanismsincluded in the finder switches terminating the subscriber line IOI. This path for applying battery potential to the control conductor .CIII of the subscriber line IOI extends from battery at the winding of the cutoff relay RI Il, by way of the winding of Rl I0 and RAIZI, to CIM.`

This application of ground potential to the start conductor Clit extending into the distributor 300 completes a circuit for` energizing the winding of the start? relay R343, this circuit extending irom ground by way ofRAI25, the control conductor CI", a resistor included in the circuit network ISI, the start conductor CJIB, RAMI, RC3 and the winding of R345 to battery.` When energized over the above-traced circuit, the start relay R305 operates to initiate operation of the distributor 300, thereby to cause the preselected idle one oi the links in the first group of links to be assigned to the use of the calling subscriber line. More particularly, upon -operating, the start relay R345 completes,` at

" all-trunks-busy conductor 032i,

RANG, a circuit for energizing the winding of the control relay R350 in series with the rotary I' magnet M300 of the rotary switch 30|, this circuit extending from ground by way of RA330, RC33I, RA305, RANG, the winding of R350, RA345, MA300, and the rotary magnet M303 to battery.` When the above-tracedseries circuit is completed, the rotary magnet M300 does not operate `due to the high series resistance of the winding of the control relay R350. However, the control relay R350 does operate. Upon operating, the control relay R350 completes, `at RA353, van alternative holding circuit for energizing the winding of the busy transfer relay R340, this circuit extending from ground by way of RA344, RA350 and the winding of R340 to battery. It is noted that the winding ofthe busy transfer relay R300 is normally energized by way of a number oi multiple circuits completed `in idle ones'oi the finder switches of the irst group of links, one of these multiple circuits being completed at this time in the ilnder switch I30 oi the link 50 and extending from ground by way of RAI, RCI45, the switch springs |35 and |01 of the busy switch SI03, the switch springs |18 and |11 of the set of switch springs SI15, the the switch springs 335 and 335 of the busy switch S334,

. RA333, and the winding of R340 to battery. Also,

it will be understood that a similar multiple circuit will be completed in each of the nder switches of idle ones ofthe links in the first group of links.

Also, upon operating, thecontrol relay R350 completes, atRAI'. a point in a-circuit traced `hereinafter for energizing the winding ofthe 4timingmelay. R313, prepares, at RA331, a point in a circuit traced hereinafter for energizing the nnder switch |30 of the link 60, 'assuming that the link 30 has been preselected by the distributor'300. Also, the control relay R350 completes, at RA35I, a circuit traced hereinafter for .energizing the windingof the start relay R|40 inthe finder switch |30 of `the preselected link 00. As previously noted, the link 60 in the rst group of links has been previously selected by the distributor 300 for the use of a calling line. Accordingly, the wipers 302 to 301, inclusive, of the rotary. switch 30| engage the contacts in the lassociated contact banks terminating the control conductors extending to the finder switch |30 of the link 60.

The circuit for energizing thewinding of the start relay RI40 in the ilnder switch |30 extends from ground by way of RA35I, the wiper 303 and associated contact of the rotary switch 30|, the finder start conductor C3I0, and the winding of R|40 to battery. When energized over the above-traced circuit, the start relay R|40 operates to complete, at RAI4I, an obvious path between the line conductors C| I6 and CI |1 of the trunk line |I extending between the finder switch |30 and the connector switch 2|5 of the link 30, and to complete, at RA|44 and RCI46, an obvious path for applying ground potential to the control conductor CI I0 of the trunk line I|5. When these paths are thus completed the connector switch 2I5 is conditioned to be operative in response to a digit dialed thereinto, in a manner more fully explained subsequently.

Also the start relay RI40 prepares at RAI42, a

circuit traced hereinafter for energizing the winding of the second test relay R325 in the distributor 300, interrupts at RAI43 a point in a path traced hereinafter for applying ground potential to the guard conductor C322, interrupts at RAI 44 and -RCI45, a point in the previously traced path for applying ground potential in the finder switch |30 to the all-trunks-busy conductor C32I, prepares at RAI41, a circuit traced hereinafter forenergizing the rotary magnet M I1I, and completes at RA|48, a circuit for energizing the vertical magnet MI10. The circuit for energizing the vertical magnet MI10 extends from' ground by way'of RA352, RA31|, RA36I, RC302, the wiper 304 and associated contact of the rotary switch 30|, the vertical conductor C320, RAI40, and the vertical magnet MI10 to battery. When energizedover the above-traced'circuit, the vertical magnet M|10 operates. Upon operating, the vertical magnet MI10 drives the carriage of the Strowger mechanism |40 of the finderA switch |30 one step in the vertical direction and completes, at MAI10, a circuit for energizing the winding ofthe step relay R310 in the distributor` 300. The circuit for energizing the winding of the step relay R310 extends from ground by way `of MAI10, the interrupter conductor C3|0 and rthewix1dingoflt31|l tbattery. V

When energized over the above-traced circuit, the step relay R310 operates, to interrupt, at RA31I, a Jpoint, in the previously` traced `circuit forV energizing the vertical magnet MI10, theres. by to cause the vertical magnet MI10 to restore.

Upon restoring, the vertical magnet MI10 interrupts, at MAI10, `the previously traced, circuit for energizingA the` winding of the step relay lR310,thereby to cause the latterrelay to restore. Upon restoring, the step' relay R310 recompletes, at RA31I, the previously traced cir- V| 40 of the finder switch |30 an additional step .in the vertical direction and -to recomplete, at

MAI10, the -previouslytraced circuit for )energizing the winding of the step relay R310 in the distributor 300.

The step relay R310 in the distributor 300 and the vertical magnet vMI10 in the nder switch |30 continue to interact in the above-described manner, thereby to cause the carriage `of the Strowger mechanism |40 of the finder switch |30 to be driven step by step in the vertical direction until the control wiper |41 engages a contact in the row of contacts associated therewith having marking ground potential thereon. In the .present instance, the carriage of the Strowger mechanism |40 of the finder switch |30 is driven two steps in the vertical direction, whereupon the con-trol wiper |41 engages the contact |40 in the row of contacts having marking ground potential thereon. A circuit is then completed for energizing the lower winding ofthe transfer relay R360 in series with the winding of the step relay R310, this circuit extending from the grounded contact |48 in the row of contacts by way of the control wiper |41, the first test conductor C'3I1, the wiper 302 and associated contact of the rotary switch: 30|,. RA366, RC361, the lowerV winding of R360, RA351, and the winding of R310 to battery. It is noted that the above--traced circuit for energizing the lower winding of the transfer relay R360 in series with the winding of the step relay R310 is completed immediately the carriage of the Strowger mechanism |40 of the ilnder switch |30 is driven the second step in the vertical direction. Accordingly, the step relay R310 does not restore incident to the restoration of the vertical magnet -M|10 at this time.

Shortly after the transfer relay R360 is energized over the above-traced circuit it operates, this relay being of the slow-to-operate type. Upon operating, the transferrelay R360 completes, at RA369, a holding circuit'traced hereinafter for energizing the upper winding thereof, interrupts, at RA366 and RC361, the previously traced circuit for energizing the lower winding thereof in series with the winding of the step relay R310, and prepares, at RA366 and RC368, a circuitl traced hereinafter for energizing the Winding of the first test relay R320. Also, upon operating, the transfer relay R300 interrupts, at RA365, a point in the previously traced original circuit for energizing the winding of the control relay R350 in series with the rotary magnet M308, an alternative circuit for energizing the winding of the control relay R350 in series with the rotary magnet M308 being completed at this time. Also, the transfer relay interrupts, at RA36| and RC362, a further point in the pre- .fracasos a point in a circuit traced hereinafter for energizing the rotary magnet Ml'll.

As previously noted, upon operating, the control relay R350 completes, at RAI", a circuit for energizing the winding of the timing relay R315, thiscircuit extending from ground by way ofv RA353, RA333, RC3, and the winding of R315 to. battery. When energized over the above-traced circuit, the timing relay R315 operates to'complete, at RA313 and `RC318, RC319, a circuit for energizing the winding of thevcontrol relayA R330, this circuit extending from ground by way of RA353, RA318, RC318, RC313, and the winding of R380 to battery. Shortly after the control relay R380 is energized by way of the above-traced circuit, this relay operates, this relay Being of the slow-to-operate type. Upon operating,` the control relay R380 completes, at RA333, a holding circuit for energizing the winding thereof, this circuit extending from ground by way of RA350, RA313, RC318, RA306, and the winding of R380 to battery. Also, upon operating, the control relay R380 interrupts, at RA382 and RC383, a point in a circuit traced hereinafter for energizing the upper winding of the control relay R330, and prepares, at RA382 and RC3", a holding circuit traced hereinafter for energizing the upper winding of the transfer relay R360. Also, the control relay R380 completes, at RA38I, the previously mentioned alternative circuit for energizing the .winding of the control relay R350 in series with the vious circuit for energizing the upper winding of the control relay R330, thereby to cause the latter relay to'operate. Upon operating, the control relay R330 completes, at RA336, a holding circuitfor energizing the lower winding thereof, this circuit extending from ground by way of RA35I, RA336, and the lower winding of R330 to battery. Also, the control relay R330 interrupts, at RA330 and RC33I, a point in the'previously traced original circuit for energizing the Winding of the control relay R350 in series with the rotary magnet M308, and completes, at RA330 and RC332, an obvious multiple alternative circuit for energizing the winding of the control relay R350 in series with the rotary magnet M308. Furthermore, the control relay R330 interrupts, at RA333 and RC334L'a point in the previously traced circuit for energizing the winding of the timing relay R315; prepares, at RA333 and RC335, a point in the previously mentioned holding circuit for energizing the upper winding of the transfer relay R330; prepares, at RA331, a point in a circuit traced hereinafter for energizing the winding of the rst test relay R320;v

and prepares, at RA338, a point in a circuit traced hereinafter for energizing the winding of the secondtest relay R325.

brates between the contacts noted for a predetermined time interval, thereby to retain the control relay R380 in its operated position during this time interval.

The previously mentioned holding circuit for energizing the upper winding of the transfer relay R330 extends from ground by way of RANG, RA333, RC335, RAI", RC384, RA338, and the upper winding of R360 to battery; while the previously mentioned circuit for energizing the ro-v tary magnet M|.1| extends from ground by .way of RA352, RA31I, RA38I, RC3, RA32I, RC322, RA320, RC321, the rotary conductor C324, RAI85, RAI51, RAI", and the rotary magnet M|1| to battery. -When energized over the above-traced circuit, the rotary magnet M|1| operates to drive the carriage of the Strowger mechanism |40`of the finder switch one step in the rotary direction and to complete, at MA|1|, an alternative circuit for energizing the winding of the step relay R310 in the distributorv 300. The circuit for energizing the winding of the step relay R310 extends from ground by way of MAI1I, the interrupter conductor C3", and the winding of R310 to battery. When energized over the abovetraced circuit, the step relay R310 operates to interrupt, at RA31I, the previously traced circuit for energizing the rotary magnet MI1I, thereby to cause therotary magnet to restore. Upon restoring, the rotary magnet M|1| interrupts, at MA|1|, the previously traced alternative circuit for energizing the winding of the step relay R310, thereby to cause the step relay to restore and recomplete, at RA31I, the previously traced circuit for energizing the rotary magnet MI1I.

The step relay R310 in the distributor 300 and the rotary magnet M|1| in the nder switch |30 continue to interact in the manner described above until the carriage of the Strowger mechanism |40 of the iinder switch |30 is rotated in `the rotary direction to the position of the contact set terminating the calling subscriber line |0|, at which time the wiper |43 of the upper wiper set engages the contact of the contact set terminating the control conductor C|04 of the subscriber line |0|, assuming that the line |0| circuit |00 in series lwith the first test relay R320 in the distributor 300. The last-mentioned circuit lextends from ground by way of RA331, the

When the previously traced circuit for lenergizing the Winding of the timing relay R315 is interrupted, the latterv relay restores, thereby to cause the weighted armature RA31B thereof to vibrate between the associated contacts RC311 Y and RC318, in order to complete intermittently the previously tra-ced holding circuit for energizing the winding of the control relay R380. It

is noted that the weighted armature RA316 viunidirectional current conducting device or copper oxide rectifier 341, the Winding 0f R320,

RC363, RA366, the wiper 302 and associated con tact of the rotary switch 30|, the first test conductor C3l1, the Wiper |43 of the upper wiper set, the associated contact terminating the control oonductor C|04 of the subscriber line IOI, C|04, RA|2| and the winding of the cutoff relay RI'I 0 to battery. i

When the cutoff relay Rl l0 in the line circuit |00 is energized by way of the above-traced cir' cuit, it does not operate due to the high series resistance of the rst test relay R320 in the distributor 300. However, the first test relay R320 does operate. Upon operatingythe first test relay R320 interrupts, at RAazl and Rom.' the previously traced circuit for energizing the rotary magnet M|1| and completes, at RA32| and RC323, a circuit for energizing the winding of the switching relay R| in the finder switch |30.

The circuit for energizing :the winding of the way of RA352, RA31I, RA38I, RC3, RA32I, RC323, the wiper 308 and associated contact of the rotary switch 30|, the conductor C323, RAI 58,

l and the winding of R|80 to battery. When energized over the above-traced circuit, the Yswitching relay RI" operates to interrupt, at RAI85, a further point in the previously traced circuit for energizing the rotary magnet M|1| and to complete, at RAI, a holding, circuit for energizing the winding thereof, this circuit extending from ground, at RAI, by way of RCI, RAIN, and the winding of R|80 to battery. Also, upon operating, the switching relay RI80 connects the trunk line |3I terminated by the upper wiper set to the trunk line I Il extending between the nder switch |30 and the connector switch 2|5. Speciilcally, the conductors C|32, CI33 and C|34 of the trunk line I3I are respectively connected, at RAI8I, RA|62 and RAI83, to the conductors CIIB, CI|1 and CII8, respectively, of the trunk line II5. When the grounded control conductor CII8 of the trunk line I|5 is connected to the control conductor CI34 of the trunk line I3I, an alternative circuit is completed for energizing the winding of the cutoff relay RI I in the line circuit |00, this circuit extending from the grounded control conductor CII8 of the trunk line |I by way of RA|53, the control conductor C|34 oi the trunk line I3I, the wiper |43 of the upper wiper set, the associated contact terminating the control conductor CI04 of the subscriber line |0I, CI04, RA|2|, and the winding of RIIO to battery. When energized over the abovetraced circuit, the cutoil.' relay RI I0 operates to complete, at RAI I3, a holding circuit for energizing the winding thereof, this circuit extending from the grounded control conductor CI04 of the subscriber line IOI by way of CI04, RAI I3, and the winding` of RI I0 to battery. Also, upon operating, the cutoff relay RI|0 interrupts, at RAI I I and RAI I 2, points in the previously traced circuit for energizing the winding of the line relay RI20, thereby to free the subscriber line c into engagement. When the switch springs 8| and |80 of the set of switch springs S|19 are actuated into engagement, a point is prepared in a path traced hereinafter for applying ground potential to the guard conductor C322. Also, the switch springs 18 and I 11 of the set of switch springs SI are actuated into disengagement and the switch springs |18 and |15 of the set of switch springs SI15 are actuated into engagement. When the switch springs |18 and |11 of the set of switch springs SI15 are actuated into disengagement, a further point in the previously traced path for applying ground potential to the all-trunks-busy conductor C32| is interrupted; and when the switch springs |18 and |16 of the set of switch springs SI15 are actuated into engagement, a point is prepared in a circuit traced hereinafter for illuminating the supervisory lamp L|28.

Also, upon operating, the switching relay RI 60 in the finder switch |30 interrupts, at RAI and RCI88, a point in a circuit traced hereinafter for energizing the release magnet lMI12, and prepares, at RAI56 and RC|61, an additional point in the previously mentioned circuit for illuminating the supervisory lamp LI28. Furthermore, the switching relay R|60 interrupts, at RA|80, a point in a circuit traced hereinafter for energizing the winding of the switching relay RI50, thereby to prevent operation oi the switching relay RI at this time; and completes, at RAI89, the previously mentioned path for applying ground potential to the guard conductor C322,

this path extending from ground by way of the y switch springs |80 and I8| of the set of switch springs S|19, RAISS, and the switch springs |85 and |84 of the busy switch |83 to the guard conductor C322. 'I'his application of ground potential to the guard conductor C322 completes a circuit for energizing the rotary magnet M308 of the rotary switch 30|, this circuit extending from the grounded guard conductor C322 by way of the wiper 305 and associated contact of the rotary switch 30|, RA353, RC355, and the winding of M308 to battery. When energized over the above-traced circuit, the rotary magnet M308 operates, thereby to condition the wipers of the rotary switch 30| to be driven one step in the rotary direction. Also, upon operating, the rotary magnet M308 interrupts, at MA'308, the previously traced alternative circuit for energizing the rotary magnet M308 in series with the winding of the control relay R350, thereby to cause the control relay R350 to restore.

Upon restoring, the control relay R350 interrupts, at RA353 and RC355, the previously traced circuit for energizing the rotary magnet M308, thereby to cause the rotary magnet M308 to restore. Upon restoring, the rotary magnet M308 drives the Wipers 302 to 301, inclusive, of the rotary switch 30| one step in the rotary direction and into engagement with the contacts in the associated contact banks terminating the control conductors extending to the lnder switch of the next link. The subsequent operation of the distributor 300 depend upon the idle or busy condition of the nder switch of the next link, in a manner more fully described subsequently.

Assuming that there are no other calls in the iirst group of lines at this time, when the line relayR|20 of the line circuit |00 associated with the subscriber line IOI restores it interrupts, at RAI 25, the previously traced path for applying ground potential to the control conductor ACI30, interrupts, at RAI22 and RCI 23, the previously traced path for applying ground potential to the control conductor CI05 of the subscriber line |0I, and completes, at RAI22 and RCI24, an alternative path for applying ground potential to the control conductor CI05, thereby to mark the subscriber line I0| as busy to the connector switches having access thereto. The last-mentioned path extends from the grounded control conductor CI04 of the subscriber line I0| by way of RAI I3, RC|24 and RAI22, to the control conductor CI05.

When ground potential is removed from the control conductor C I 80, the previously traced circuit for energizingvthe winding of the start relay R345 in the distributor 300 is interrupted, thereby to cause the start relay R345 to restore. Upon restoring, the start relay R345 interrupts, at RA346, the previously traced original circuit for energizing the Winding of the control relay R350 in-series With the rotary magnet M308. Also, when the control relay R350 restores, as previously noted. it interrupts, at RA363, a further point in the circuit for energizing the winding thereof in series with the rotary magnet M308. Also, at RA363 and RC3, the wiper 306 or the rotary switch 30| is connected by way of the seit-interrupting contact MA308 and the rotary magnet M308 to battery, this connection extending. from the wiper 385 by way of RA353, RC354, RA345, MA308, and the rotary magnet M308 to battery.

In the event'the finder switch of the next link in the first group is busy at this'timeground potential appears upon the guard conductor thereof, corresponding to the guard conductor C3220! the iinder switch |30, as previously noted, thereby to complete a circuit extending by way l of the previously traced connection for energizing the rotary magnet M308. When thus energized, the rotary magnet M308 operates to condition the wipers. of the rotary switch 30| to be driven an additional step in the rotary direction and to interrupt, at MA308, the previously traced vcircuit for energizingthe rotary magnet M308.

When the previously traced circuit for energizing the rotary magnet M308 is interrupted, the rotary magnet restores, thereby to drive the wipers of the -rotary switch 30| an additional step in the rotary direction. The rotary magnet M308 startconductorC3I3 extending to the distributor 300 is connected, together with the start conductor C3I5, to the conductor C321 extending to the distributor 3|2. Hence; at this time, the distributor.3|2 is operative to assign idle links in the second group of links to the use of callingV plete, at RAI43, an alternative path for applying ground potential to the guard conductor C322, this path extending from ground by way of continues to operate in the above-described manner in order to cause the wipers of the relay switch 30| to be driven step4 by step in the rotary direction until the iincler switch -of an idle link in the iirst group ci.' links is found. When the iinder switch of an idle link in the first group of links is found, further operation of the rotary Vmagnet M308 is arrested, due to the fact that no ground 'potential appears upon the guard conductor thereof, corresponding to the guard con- ,event that an idle link is available in the iirst group of-links, due to the fact that the busy transfer relay R340 is retained in its operated position at this time only in the event that ground potential is present upon the all-trunksbusy conductor C32|, which condition obtains only in the event that there is an idle link available in the ilrst group of links. In the event that all oi the links in the iirst group of links are busy at this time, no ground potential appears upon the all-trunks-busy conductor 032|, whereby the circuit for energizing the winding of the busy transfer relay R340 is interrupted in order to cause the busy transfer relay R340 to restore. Upon restoring, the busy transfer relay R340 interrupts, at RA344, a further point in the alternative holding circuit for energizing the winding thereof, interrupts, at RA345, a point in the previously traced circuit for energizing the rotary magnet M308, thereby -to prevent operation of the rotary magnet M308, andinterrupts, at RA34I and RC343, the connection between the start conductor C3||` and the winding ofthe start relay H1345. Also, upon restoring, the bulsy transf fer relay R340 connects, at RA34| and RC342,

the switch springs |80 and |8I of the set of switch springs SI19, RA|43, and the switch springs |85 and |64 of the busy switch S|83 to the guard conductor C322. This application of ground'potential to the guard conductor C322 insures that the distributor 300 will not operate tov select the busy link 60 at this time. Also, upon restoring, the start relay, RI40 interrupts, at`

RAI 41, a further point in the previously traced circuit for energizing the rotary magnet MI'II,

. interrupts, at RAI48, a further point in the previously traced circuit for energizing the vertical magnet MI10, interrupts, at RAI42, a point in the previously mentioned circuit for energizing the winding of the second test relay R325 in the distributor 300, and completes, at RAI44 `and RC|45, the previously mentioned .circuit for illuminating the supervisory lamp LI28, this circuit extending from ground by way of RAI44, RCI45, the switch springs |86 and |81 of the busy switch SI83, the switch springs |18 and |16 of the set ofV switch springs SI15, RAISE, RC|61 and LI28 to battery. The illumination of the supervisory lamp L|28 indicates tothe exchange attendant that the link 60 is busy upon a call routed therethrough. i

Also, upon restoring, the control relay R350 in the distributor 300 interrupts, at RA352, the previously traced original' circuit for energizing the switching relay RI60 in the iinder switch |30, interrupts, at RA351, a further point in the previously traced circuit for energizing the lower winding of the transfer relay R360 in the distributor 300, and interrupts, at RA356, a point in the previously traced circuit for energizing the upper winding of the transfer relay R360 and a point in the previously traced holding circuit for energizing the winding of the control relay R380, thereby to cause thetransfer relay R360 and the control relay `R380 to restore. Upon restoring,

the transfer relay R360 interrupts, at RA333, a l further point in the holding circuit for energizing the upper winding thereof, interrupts, at RA36$ and RC358, a point in the previously traced circuit 4for energizing the Winding of the first test relay R320, and prepares, at RA366 and RC361,

a point inthe previously traced circuit for energizing the lower winding thereof.. Also, upon the conductors C328 and C321 extending to the restoring, the transfer relay R360 prepares, at RA365, a point in the previously traced original circuit for energizing the winding of thecontrol relay R350 in series with the rotary magnet M308,.interrupts, at RA36| and RC364, a further point in the previously traced original circuit for energizing the winding of the switching relay RISO in the finder switch |30, and prepares, at

RA38I and RC382, a point in a circuit for energizing the vertical magnet in the lnder switch of a selected link when the distributor 300 operates to select an idle link in the first group of links for the use of a calling line.

Upon restoring, the control relay R380 interrupts,'at RA386, a further point in the holdingl circuit for energizing the winding thereof, interrupts, at RA385, a point in the holding circuit for energizing the upper winding of the control relay R330, thereby to cause the latter relay to restore, and interrupts, at RA382 and RC384, a further point in the holding circuit for energizing the upper winding of the transfer relay R360. Also, the control relay' R380 prepares, at RA382 and RC383, a point in a circuit traced hereinafter for energizing the upper winding of the control relay R390, and interrupts, at RA38I, a point in the previously traced alternative circuit for energizing the windingof the control relay R350 in series with the rotary magnet M308.

Upon restoring, the control relay R330 interrupts, at RA336, a further point in the previously traced holding circuit for energizing the lower winding thereof, interrupts, at RA331, a further point in the previously traced circuit for energizing the winding of the first test relay R320, Y

and interrupts, at RA338, a point in the previously mentioned circuit for energizing the winding of the second test relay R325. Also, the control relay R330 interrupts, at RA333 and RC335, a further point in the holding circuit for energizing the upper winding of the transfer relay R360, prepares, at RA333 and RC334, a point in the previously traced circuit for energizing the winding of the timing relay R315, interrupts, at RA330 and RC332 a. further point in the previously traced alternative circuit for energizing the winding of the control relay R350 in series with the rotary magnet M308, and prepares, at RA330 and RC33I, a point in the previously traced original circuit for energizing the winding of the control relay R350 in series with the rotary magnet M308.

Upon restoring, the first test relay R320 interrupts, at RA32| and RC323, a further point in the previously traced original circuit for energizing the winding of the switching relay R|60 in the finder switch |30, and prepares, at RA32I and RC322, a point in a circuit for energizing the rotary magnet in the nder switch of a preselected link. At this time, the distributor 300 is completely released for further use and the subscriber substation A is operatively connected by way of the previously traced circuit to the connector switch 2| 5. 4

As previously noted, as soon as the finder switchY operates to seize the calling subscriber line |0I, ground potential is applied therein to the guard conductor` C322, thereby to complete the previously traced path for shortcircuiting the winding of the control relay R350 in order to cause the control relay R350 to restore and initiate the release of the distributor 300. It is noted that it is not possible to reoperate the control relay R350 until the distributor 300 is completely released in spite of the fact that there may be present a calling line in the first group of lines which causes the start relay R345 to remain in its operated condition, due to the fact that, upon restoring, the control relay R350 interrupts, at RA359, the previously M308, and the originalcircuit for energizing the winding of the control relay R350 in series with the rotary magnet M308 is not recompleted un-v til subsequent to the restoration of the transfer relay R360 and the control relay R330, as previously explained. Accordingly, the distributor 300 is completely released each time a finder switch of a link selected thereby operates to find a calling line in spite of the fact that the start relay R345 therein remains operated, due to the presence of other calling lines in the first group of lines.

In the event another calling line is present in the rst group of lines at this time, the start relay R345 in the distributor 300 remains in its operated position, and, when the transfer relay R360 and the control relay R330 restore, the previously traced original circuit for energizing the control relay R350 is recompleted, assuming that the rotary magnet M308 has already oper" ated to cause the rotary switch 30| to find an idle link in the first group of links. The control relay R350 then operates, thereby to cause the finder switch of the previously selected link to operate and seize the calling subscriber line in the rst group of lines, as explained above.

As previously noted, the distributor 300 is operative to cause the finder switch of a selected link in the first group of links, such as the nder switch |30 of the link 60, to operate and seize a calling line in the second group of lines, which condition may arise when all of the links in the second group of links are busy. In this event, the distributor 3|2 operates, thereby to cause the conductors C321 and C328 therein to be connected togetherin a manner similar to that previously explained, incident to the restoration of the busy transfer relay R340 in the distributor 300 when all of the links in the rst group of links are busy. At this time, ground potential applied to the start conductor C3|5 is extended by way of the conductor C321 and the distributor 3|2 to the conductor C328, in order to cause the start relay R345 in the distributor 300 to be energized and to operate in the previously described manner. The subsequent operations of vthe distributor 300 and the finder switch |30 of the link 60, incident to the operation of the start relay R345 in the distributor 300,'are the same as previously described, assuming that the calling line in the second group of lines is also accessible to the upper wiper set of the Strowger mechanism |40 of the finder switch |30.

Furthermore, the nder switch |30 of the link 60 is operative in a manner substantially identical to that previously explained to find a calling line in either the first group of lines or the second group of lines and accessible to the lower wiper set of the Strowger mechanism |40 thereof. However, in this case, when the carriage of the Strowger mechanism |40 of the finder switch |30 is rotated in the rotary direction to the position of the contact set terminating the calling subscriber line, battery potential is encountered by the wiper |46 in the lower wiper set appearing upon the contact terminating the control conductor of the calling subscriber line. This application of battery potential to the wiper |46 completes the previously mentioned circuit for energizing the winding of the second test relay R325 in the distributor 300, this circuit extending from ground by way of RA338, the unidirectional current conducting device or copper oxide rectifier time second test conductor` C320, RAI42,-and the control conductor CI30 of the trunk line |30 -to battery potential appearing upon the wiper |40. When overthe above-tracedv circuit.

test relay R025 operates to interrupt. at M320 and RC3", a point in the previously tracedcircuit for energizing the rotary magnet MIII `in the nder switch |30, thereby to arrest further operation of the iinder switch. Also. upon operating, the second test relay R325 completes, at RA320 and RC020, the previously mentioned circuitior energizing the winding of the switching relay R|50 in the finder switch |00, thisfcircuit` extending from ground by way of RA302, RM'II, `RA30|, RC304,RA32|, RC322, RA320. RC320, the wiper 301 and associated contact `of the rotary switch 30|, the conductor C320, v

RAI, and the winding of RI" to battery.

When energized over the above-traced circuit,'the. switching relay R| operates 'to interrupt, -at RAI 51, a further point in'thepreviously traced circuit for energizing the rotary magnet MIlI, and to complete, at RAI, a path for applying R|00 is not operated. Hence, theilnder switch ground potential to the guard conductor C322.

The path for applying ground potential to the guard conductor C322 extends from ground by `way of the swltchsprings |80 and I0| of the set Y of switchspringsSlll, RAISE, and the switch springs |85 and |04 of the busy switch- S|03 to 30 the guard conductor C322. Thisapplication of ground potential lto the guard conductor C322 causes the distributor 300 to be released and the rotary switch therein to `operate and select an idle link in the iirstgroporlinks, aspreviously explained. l

Also, upon operating, the switching relay R150 interrupts, at RAl55, a pointin the previously traced circuit forv energizing the winding of the switching relay RIBO, and completes, at RAI 54, a holding circuit for energizing the winding thereof this circuit extending fromA the grounded control conductor CI I3 of the trunk line ||5 by way of` RA|54 and the winding of R|50 to battery. Finally, the switching relay RI50 connects the trunk line extending to the lower wiper set of the Strowger mechanism to the trunk line ||5.^ More speciilcally, the conductors C|38, CI3I and C |38 of the trunk line |35 are respectively connected at RAI 5|, RA|52 and RA|53 to 50 the conductors CI I6, CI I1 and CI I8, respectively,

VOf the trunklinei I5. When the trunk line |35 is connected to the trunk line ||5, the line circuit individually associated with thek calling subscriber line and the connector switch 2|5 operate in the previously `described manner.

It is noted that there is a possibility that the upper and lower wiper sets ofthe Strowger mechthe previously traced circuit for energizing the winding of the switching relay RI50, thereby to prevent operation' oi' the switching relay R|50. Accordingly, under this condition, the switching `relay R|00 is operated andthe switching relay |30 operates to find the calling line accessible to the upper wiper set of the Strowger mechanism |40 thereof in preference to the calling line accessible to the lower wiper set -of the. Strowger mechanism |40 thereof. ,g

It is noted that, incident to operation of the `finder switch |30, the Wipers |43 and |46 in the upper and lower wiper sets, respectively, of the Strowger mechanism |40 may engage contacts in the contact sets in the associated contact bank terminating the controlconductors or subscriber lines having either ground or booster battery potential appearing thereupon; ground potentlal appearing upon the control conductors of the subscriber lines whenthe subscriber lines are busy. and booster battery potential appearing upon the subscriber lines when the subscriber lines are being metered. When the wiper |43 of the upper wiper set of the Strowger mechanism |40 engages a contact having `ground potential appearing thereupon,4 a` path is completed for short-circuiting the winding of the ilrst test relay R320 in the distributor 300, this circuit extending irom the grounded control conductor of thesubscriber line, by way of the Wiper |43 and the associated contact, CI34, the ilrst'test conductor-CM1, the wiper 302 and associated contact ofthe rotary switch 30|, RA360, RC363, the winding of R320, the copper oxide rectifier 341, and `RA33`| to ground. When the wiper |43 of the upper wiper set of the Strowger mechanism I 40 engages a contact having booster battery potential appearing thereupon, a circuit is completed substantially identical to the above-traced path, tending to energize the winding of the first test relay R320. However. the copper oxide rectil iler 341 is so connected and arranged that current is prevented from traversing this circuit in a direction extending from the wiper |43 to ground at R'A`33'I.V Accordingly, the ilrst test relay R320 is not effectively energized. Thus, the first test relay R320 does not operate when the wiper |43 of the upper wiper set of the Strowger mechanism |40'cngages a contact terminating the control conductor of a subscriber line having either ground or booster battery potential appearing thereon.

In a similar manner, a path is completed for short-circuiting the winding of the second test relay R325 when the wiper '|46 in the lower wiper set of the Strowger mechanism A|40 engages a contact terminating a control conductor of a subscriber line having ground potential appearing thereon; and a circuit is completed tending to energize the winding of the second test relay R325 when the wiper |45 engages a contact terthe Strowger `mechanism |40 complete the previouslytraced circuits for respectively energizing the windings of the first and second test relays R320 and R325, respectively, thereby to cause both of these test relays to operate. Upon operating, the iirst test relay R320 completes, at RA32| and RC323, the previously traced circuit lor energizing the winding of the switching relay RI60, thereby to causethe switching relay R|80 minating a control conductor of a subscriber line having booster battery potential appearing thereon. However. the copper oxide recticr 348 prevents the winding of the second test relay R325 from being effectively energized in the last-mentioned case. Hence, the arrangements of the copper oxide rectiilers 341 and 348 in the circuits for respectively energizing the windings of thefirst and second test relays R320 and R325, respectively, prevent false operation of the iinder switch |30 andthe consequent seizure thereby to operate, and interrupts, at RA32| and RC322, 75 01' busy Subscriber line having booster battery thereof.

In the foregoing descriptiony of the operation of theilnder switch |30 of thelink 00 to seize the calling subscriber line it was assumed uthat the nder switch` |30 operated properly to seize this calling subscriber line. However, it

may occur that the finder switch |30 fails tol operate properly to seize the calling subscriber line |0| when the operation thereof is initiated by the distributor 300, dueto the fact that the finder switch |30 has become temporarilyinoperative. In this event, the iinder switch |30 fails to. seize the calling subscriber line |0|. Accordingly. ground potential is not applied in the ilnder switch |30 tothe guard conductor C322 in order to cause the distributor 300 to be released, as previously explained.. Hence, after a `predetermined time interval, the vibratory armature RA313 of the timing relay R315 in the distributor 300 `assumes an intermediate position with respect to the associated contacts RC3" and RC313, thereby to interrupt the previously traced holding circuit for energizing the winding of the control relay R330 in order to cause the control relay R300 to restore. Upon restoring, the control relay R300. interrupts, at RA302 and RC334, the previously traced holding circuit for energizing the upper winding of the transfer relay R300, and completes, at RA382 and RC333, a point in the previously mentioned circuit for` energizing the upper winding of the control relay R330. The circuit for energizing the upper winding of the control relay R330 extends from ground by way of RA356, RA333, RC335, RA302, RC333, and the upper winding of R390 to battery. When energized over the above-traced circuit, the control relay R390 operates to complete, at RA332. a holdingcircuit for energizing the lower winding thereof, this circuit extending from the grounded conductor C330 by way of the switch springs 338 and 331 of the busy switch S334,

RA332 and the vlower winding of R330 to battery. It is noted that ground potential appears upon the conductor C330 in the distributor 312 so long as ground potential appears upon the alltrunks-busy conductor associated with the finder switches ofthe links in the second group of links, just as ground potential appears upon the conductor C323 in the distributor 300 so long as ground potential appears upon the al1-trunksbusy conductor C32| associated with the finder switches of the links in the iirst group of links. Also, upon operating, the relay R390 completes. at' RA33I, a path for short-circuiting the winding of the control relay R350, this path extending from the upper terminal of the winding of R350 by way of RA39I, RA353, RC355, MA300, RA345, and the Winding of R350 to the upper terminal thereof. When the winding of the control relay R350 is thus short-circuited, the control relay R350 restores to interrupt, at RA353 and RC355, a point in the previously traced path for short-circuiting the winding thereof, and to complete, at RA353 and RA354, an alternative path for short-circuiting the winding thereof. The alternative path for short-circuiting the winding of the control relay R350 extends from the upper terminal of the winding of R350 by way of RA33I, RA353, RC354, and the Winding of R350 to the upper terminal thereof. Also, upon restoring, the control relay R350 interrupts, at RA353, a 'point in the previously traced alternative circuit for energizing the winding of the busy transfer relay R340.

'assassin y upon' operating, the control relay R300 interrupts, at RA303, the previously traced orig v inal circuit for energizing the windingofthe busy transfer frelay R340, kand interrupts, at RA334, the normal connection between the conductor C320 extending-into the distributor 3|2 and the winding of the busy transferrelay R340, thereby to cause the busy transfer relay R340to restore and to insure that it remains inv-its restored position. Upon restoring, the busytransfer relay R340 completes..A at RA34| Iand RC342, the previously mentioned connection between the conductors C321 and C320, extending to the distributor 3|2, therebyy to cause the distributor 3|2 to assign links in the second group of links to the use of calling lines in both the first and second groups of lines, as previously explained.

Also, upon operating, the control relay R300 completes,` at RA392, a circuit for illuminating the supervisory lamp. 1.300, this circuit extending from the grounded conductor C330 by way of the switch springs 330 and 331 of thebusy switch S334, RA332, and the lamp L300 to battery. Illumination of the supervisory lamp L30! indicates to the exchange attendant that the distributor 300 is locked out of service.y The release" of the remainder of the operated relays in the distributor 300, incident to the restoration of the control relayR350 and the busy transfer relay R340, is the same as that previously described. At this time, the distributor 300 is locked out of service, as previously noted.

It is noted that the distributor 300 remains locked out of service until the busy switch S334 is operated away from its normal position and returned thereto, which switch will no t be thus operated until the defective finder switch of one of the links in the iirst group of links is found and again placed in working order. When the busy switch S334 is operated away from its normal position, the switch springs 331 and 333 are actuated into disengagement, thereby to interrupt the previously traced holding circuit for energizing the lower winding of the control relay R330 in order to cause the control relay R300 to restore. Upon restoring, the control relay R390 reconnects, at RA394, the conductor C320 extending into the distributor 3 |2 to the winding of the busy transfer rel-ay R340, and prepares, at RA393, a point in the previously traced original circuit for,` energizing the winding of the busy vtransfer relay R340 by way of the all-trunksbusy conductor C32I. When the busy switch S334 is returned to its normal position, there is completed at the switch springs 335 and 333 thereof the previously traced original circuit for energizing the winding of the busy transfer relay R340 by way of the all-trunks-busy conductor C32I, in the event one oi' the links in the first group of links is idle at this time, as previously explained.

It is noted that the nder switch |30 of the link 60 embodies an arrangement for causing the distributor 300 to select another idle link in the first group of links for the use of the calling subscriber line |0| in the event that the nder switch |30 of the selected link 50 in the -ilrst group of links fails to find the calling line 0| incident to the operation thereof. More particularly, the set of switch springs SI14 in the finder switch |30 is actuated into engagement when the carriage of the Strowger mechanism |40 of the finder switch |30 is driven eleven steps in the rotary direction away from its normal position, dueto the failure of the nder switch m wand-the umg une m. when the set oi' switch springs S|14 is actuated into engagement, a path is completed for applying ground the rotary switch 30| therein to operate and select another idle link in the rst group of links for the use of the'calling subscriber line III, in the previously described manner.

It is noted that the iinder switch |30 of the link 80 may be rendered busy by operating the busy-switch SI83. When the busy switch S|33 is operated, the switch springs |88, |81 and |84, |85 thereof are actuated into disengagement, and the switch springs |88, |84thereof are actuated into engagement. Whenthe switch springs |38 and |81 of the l'busy switch S|83 are actuated into disengagement, the previously tracedpath for applying ground potential in the nder switch |30 to the all-trunks-busy.conductor.I C32| is interrupted; when the switch springs |84 and |85 rof the busy switch S|83 are actuated into dis- /ground potential to the guard conductor C322 exends from ground by way of RAI44, RCI, and the switch springs |88 and |84 of the busy switch /S|83, to the guard conductor C322. ,This application of ground potential tothe guard conductor C322 marks the link 60 as busy, thereby to prevent the distributor 300 from selecting the link 60 in the iirst group of links. or causes the rotary switch 30| in the distributor 300 to operate and select another idle link in the first group of links in the event that the distributor 300 has previously operated to select the link 80 prior to the operation of the busy switch S|83 therein. In the event the distributor 300 has operated to select the link 60 in the iirst group of links prior to operation of the busy switch S|83 therein, as explained above, the application of ground potential to the guard conductor C322, incident to the operation of the busy switch SI83, causes the rotary switch 30| in the distributor 300 to operate and -select another idle link in the nrst group of links. Specically, this application of ground potential to the 'guard conductor C322 completes the previously traced circuit for energizing the rotary magnet M308 of the rotary switch 30| in the.distributor 300. The operation of the rotary magnet M308 to cause the rotary switch 30| to select an idle link in the rst group of links is the same as that previously explained.

In View of the foregoing explanation of the mode of operation of the distributor 300 to assign idle links in the first group of links to the use of calling lines, it willbe understood that the distributor 3|2 is operative in an identical manner to assign idle ones of the links in the 75 second groups of links to the use of calling lines. Again itis noted that the links in the ilrst group of links are normally assigned to the usepof calling'lines in the first group of lines, but are as- 5 Signedtotheuseoi'callinglinesinboththefirst group of lines and the second group of lines when all ofthe links in the second group of lines are busy; while the links in the second group of links are normally assigned to the use of the calling lines in the second `group of lines, but are assigned to the use of calling lines in both the iirst group of lines and the second group of lines when :il of the links in the ilrst group of links are Further itis noted that the lines in the'` first group of lines are terminated in the first five levels of the Strowger mechanisms of the iinder switches in the ilrst group of links;4 while the lines in the second group of lines are terminated in thesecond tive levels of the Strowger mechanisins of the iinder switches in the first group v of links. Conversely, the lines in the first group of lines are terminated in the second' five levels of the Strowger mechanisms of the finder switches in the second group'of links; while the linesin the second group of lines are terminated in the iirst iive levels of the Strowger mechanisms of the finder switches in the second group oi' links. Ihus it will be understood that the levels 2, 3, 4 and 0 in the Strowger mechanisms of the iinder switches in the ilrst group 4of links correspond respectively to the levels I0, 3, 8, 'l and-0 in vtheStrowger mechanisms of the finder switches in the second group of links, the

levels mentioned terminatingthe lines in the first group of lines; while the levels 8, 1, 8, 9 andV |0 in the Strowger mechanisms of the finder switches in the rst group of links correspond respectively to the levels 5, 4, 3, 2 and v|in the 40 Strowger mechanism of the finder switches in the second group of links, the levels mentioned ierminating the lines in the second group of lines. iliccordingly, it will be understood that the iifth `and sixth levels in the Strowger mechanisms of the iinder switches in the iirst group of links respectively correspond to the sixth and fifth levels in the Strowger mechanisms of the finder switches in the second group of links.

` Considering now the operation of both the distributor 300 and the distributor 3|2, it is noted that a iirst path or blocking circuit is provided for applying ground potential to the contacts in the iii'th level of the Strowger mechanisms of the finder switches in the iirst group of links, which path extends, wh'en completed, from ground by way ofRA381, C20I, RA340' and C204 to the level mentioned; while a second path or blocking circuit is provided for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the inder switches in the second `group of links, which path extends, when completed, from ground by way of RA381, C202, RA340 and C203 to the level mentioned. Further it is noted that the control relay R380 and the busy transfer relay R340 in the distributor 300 respectively correspond to the control relay R380 and the busy transfer relay R340' in the distributor 3| 2;

As previously explained, the busy transfer relay 7|- R340 in the distributor 300 occupies its operated the. busy transfer relay am' in the distributor SI2 occupies its operated positionwhile there is an idle'link in the second group of links or while the distributor is operating while the control relay R300 inthe distributor I2 occupies its.

operated position only while the distributor SI2 is operating. Accordingly, the first path for applying ground potential vto the contactsin the fifth level of the Strowgermechanisms of the finder switches in the first group of links is completed wh'en the control relay R000 in the distributor 300 and the busy transfer relay R340' in the distributor SI2 occupy their operated positions, which' condition prevails while the distributor 000 lsoperating, and when-there is an idle link in the second group of links or while the distributor )I2 is operating; while the second path for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the finder switches in the second group of links is completed when the control relay R380', in the distributor 3I2 and th'e busy transfer relay R340 in the distributor 300` occupy their operated positions, which condition prevails while the distributor 3I2 is operating, and when there is an idle link in the first group of links or while the distributor 300 is operating.

When the first path for applying ground potential to the contacts in the fifth level of the Strowger 4mechanisms of the finder switches in th'e first group of links is completed, the Strowger mechanisms of the finder switches of the links in the first group of links are positively prevented from operating beyond the fifth level thereof due to the presence of ground potential upon the cony tacts in the fifth level thereof, thereby rendering the lines in the second group of lines non-selectable by the Strowger mechanisms of the finder switches in the first group of links at this time. More specifically, the application of ground potential to the contacts in the fifth level of the Strowger mechanisms of the finder switches in the first group of links is effective to causev operation of the transfer relay R360 in the distributor 300 and the consequent arresting of the operation of the vertical magnet in the Strowger mechanism of the finder switch of the link assigned for use at this time, in the event the Strowger mech.. anism of the finder switch of the link assigned for use at this timev is operated to the fifth level thereof. The rotary magnet in the Strowger mechanism of the finder switch of the link assigned for use at this time is then operated, thereby to cause the Strowger mechanism of the finder switch of the link mentioned to seize a calling line in the fifth level thereof or the finder switch of the last-mentioned link to be released in the manner previously explained.

Similarly, when the second path for applying ground potential to the contacts in the fifth level of the `Strowger mechanisms of the finder switches in the second group lof links is completed, the Strowger mechanisms of the finder switches ofthe links in the second group of links' are ypositively prevented from operating beyond the'fth level thereof due to the presence of ground potential upon the contacts in the fifth level thereof, thereby rendering the lines in thel -aasaasc not shown, in the distributor m and the consequent arresting of the operation of the vertical magnet in the Strowger mechanism of the finder switch of the link assigned for use at this time, in

the event the Strowger mechanism of the finder switch of the' link assigned for use at this time is operated to thefifth level thereof. The rotary magnet in the Strowger mechanism of the finder switch of the link assigned for use at this time is then operated, thereby to cause the Strowger mechanism of the finder switch of the link mentioned to seize a calling line in th'e fifth level thereof or the finder switch of the last-mentioned link to be released in the manner previously explained. r

In view of the foregoing explanation of the mode of operation of the distributors 300 and) I 2, it will be understood that, when all of the links in the firstgroup of'links are rendered busy and the distributor 300 is released, the busy transfer relay R340 in the distributor 300 restores, thereby to transfer the rst start conductor C3I6 lto the distributor 3|! and t0 interrupt, at RAMI),

the second path for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the finder switches in the second group of links, thereby to render the Strowger mechanisms of the finder switches in the second group of links operative to seize a calling line in either the second group of lines or the first group of lines; similarly, when all of the links in the second group of links are rendered busy and the distributor 3I2 is released, the busy transfer relay R340' in the distributor 3I2 restores, thereby to transfer the second start conductor C3I5 to the distributor 300 and to interrupt, at RA340', the first pathi for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the finder switches in the first group of links, thereby to render the Strowger mechanisms of the finder switches in the first group of links operative to seize a calling line in either the first group of lines or the second group of lines. Further it is noted that, when the distributor 300 is not operating, vthe control relay R380 therein restores, thereby to interrupt, at RA38`I, the first path for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the finder switches in the first group of links; similarly, when the distributor 3I2 is not operatingl the control relay R380 therein restores, thereby to interrupt, at RA38'I, the second path for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the nder switches in the second group of links.

In view of the foregoing description of the mode of operation of the distributors 300 and 3 I 2, it will be understood that Athe connection and arrangement thereof positively prevent simultaneous seizure of a calling line in one of the groups of lines by the Strowger mechanisms of finder switches of two links in the respective groups of links incident to the abandonment of a call on a line in the other of the groups of lines. For example, in the event calls are initiated on two lines in the respective first and second groups of lines, operation of the distributors 300 and 3| 2 are initiated, whereupon operation of the Strowger mechanisms of finder switches of two links in the respective groups of links are initiated. Now in the event the call on the line in the second group of lines is abandoned, the Strowger mechanism of the finder switch in the second group of links is arrested when it is operated to the fifth level thereof due to the completed second path for applying ground potential to the contacts in the fifth level of the Strowger mechanisms o1' the finder switches in the second group of links; accordingly, there is no interference by the Strowger mechanism of the finder switch of the link inthe second group of links with the operation ofthe 'Strowger mechanism of the finder switch of the link in the first group of links. On the other hand, in the event the call on the line in the rst group of lines is abandoned the Strowger mechanism of the nder switch in the iirst group of links is arrested when it is operated `to the iifth level thereof due to the completed rst path for applying ground potential to the contacts in the fifth level of the Strowger mechanisms of the finder switches in the first group of links; accordingly, there is no interference by the Strowger mechanism of the finder switch of the link in the first groupV of links with the operation oi 'the Strowger mechanism of the finder switch of the link in the second group 4of links. In other words, the distributors 300 and 3|2 are so connected and arranged that a line in the first group of lines is not selectable by the ilnder switch of a link in the vsecond group of links while the distributor 300 is operating; while a linein the second group of lines is not selectable by the finder switch of a link in the first group of links while the distributor 3I2 is operating.

Continuing now with the operation of the connector switch 2I5 to extend a call from the subscriber substation A to the subscriber substation B,`when the iinder switch |30 operates to seize the calling subscriber line I I, the connector switch 2I5 is rendered operative in response to digits transmitted thereto from the subscriber substation A. t

The subscriber at the substation A then dials the digits ofthe directory number of the called subscriber substation B at the dial mechanism at the substation A, thereby to transmit a number of series of impulses by way of the subscriber loop circuit to the connector switch 2I5, in order to causethe connector switch 2|5 to operate, in the usual manner, and seize `the called subscriber line 230. In the event the called subscriber line 230 is busy, ground potential appears upon the control conductor C234 thereof, thereby to causethe connector switch `2| 5 to operate and return busy tonecurrent over the loop circuit extending to the calling subscriber substation A,

in the usual manner. On the other hand, in the event the called subscriber line 230 is idle, battery potential appears upon the control conductor C234 thereof.

The connector switch 2I5 then operates to cause direct `ground potential to be applied to the control conductor C234 of the telephone line 230, thereby to mark the telephone line 230 busy to the connector switches having access thereto.

After seizing the called subscriber line 230, the connector switch 2|5 operates to cause ringing current to be projected over the line conductors C23| and C232 of the subscriber line 230 in the usual, manner, thereby to cause the ringer at the called substation B to operate. When the subscriber at the substation B answers the call by removing the telephone receiver of the telephone instrument thereat from its` associated switchhook, a loop circuit is completed by way of the line conductors of the subscriber line `230 to the connector switch 2|5, thereby tocause a battery reversing relay in the connector switch 2|! to operate in the usual manner. Also, the connector switch 2|! operates to complete a connection between the calling subscriber loop circuit extending thereto from the subscriber substation A and the called subscriber loop circuit extending thereto from the substation B, whereupon an established connection is completed between the calling subscriber substation A and the called subscriber substation B.

The release of the established connection between the subscriber substations A and B is under the control of the subscribers thereat and. when both oi the subscribers replace the receivers o! the telephone instruments upon their associated switchhooks at .the substations A and B, the connector switch 2li rst releasesf When the connector switch 2|5 is released, ground potential is removed from the control conductor C|I8 of the trunk line II5. When ground potential is removed from` the control conductor xs CI I8 of the trunk line I I5, the previously traced circuit for energizing the. winding of the switching relay RI in the finder switch |30 is interrupted, therebyw to cause the latter relay'to `restore. Uponrestoring, the switching relay RI" prepares, at RAIBS, a point in the previously traced circuit for energizing the rotary magnet MI1I, interrupts, at RAIGS, a point in the previously traced path for applying ground potential to the guard conductor C322, interrupts, at RAI, a further point in the holding circuit for ,energizing the winding thereof, prepares, at RAI80, a point in the previously tracedcircuit for` energizing the winding of the switching relay RISO, and interrupts, at RAIBI, RAISZand RAIN, the connection between the trunk line II5` and the trunk line I3I. Also, upon restoring, the switching relay RI60 interrupts, at RAISE and RC|61, the previously traced circuit for illuminating the supervisory lamp LI28, and completes, at RAISE and RCIG8, the previously mentioned circuit for energizing the release magnet MHZ. The last-mentioned circuit extends from ground by way of RAI44, RCI45, the switch springs |80 and |81 of the busy switch |83, the switch springs |18 and |16 of the set of switch springs SI15, RAISG, RCI68, RAISB, and the release magnet MI12 to battery. When energized over the above-traced circuit, the release magnet MI12 operates, thereby to release the carriage of the Strowger mechanism |40 and to cause it to be returned to its normal position. When the carriage of the Strowger mechanism is returned to its normal position, the setsof switch springs SI15 and SI19 are actuated. More particularly, the switch springs` |80 and |8I of the set of switch springs SI19'are actuated into disengagement, thereby to interrupt a further point in the previously traced path for applying ground potential to the guard conductor C322; the switch springs I8I and |82 are actuated into engagement, thereby to connect the guard conductor C322 to the control conductor CI I8 of the trunk line |I5; the switch springs |18 and |18 of the set of switch springs SI15 are actuated into disengagement, thereby to interrupt the previous- 1y` traced circuit `for energizing `the release magnet MI'I2; and the switch springs |11 and |18 of the set of switch springs SI15 are actuated into engagement, thereby to complete the previously traced path for applying ground potential in the finder switch |30 to the al1-trunksbusy conductor C32I. The previously mentioned connection between the guard conductor C322 and the control conductor CI I8 of the trunk line 14 V III extends from the guard conductor C322, by way oi .the switch springs lll and ill of the busy switch Si, RAI, and the switch springs Ill and i8! of the set o! switch springs Bill to the control conductor CHI of the trunk line I Il. The connection of thev guard conductor C822 tothe control conductor CI Is of the trunk line lill insures 4that the link Il will not be se lected by' the distributor III for the use of Va calling one ot the lines unless both the finder switch I" and the connector switch 2l! thereof are completely released. At this time, the finder switch III is completely released. Accordingly, the link Il is completely released and is available to be selected by the distributor l for the use of a calling one of the lines.

When ground potential is removed from the control conductor Cl Is of thetrunk line III, the previously traced circuit for energizing the winding of the cuto relay Rill in the line circuit III individually associated with the subscriber line I Il is interrupted, thereby to cause .the latter relay to restore.. Upon restoring, the cutoi! relay RI Il interrupts, at RAI I3, a further point in the holding circuit for energizing the winding thereof and prepares, at RAIII and at RAID, points inthe previously traced circuit for energizing the winding of the linerelay RIN. At this time, the line circuit Ill is completely released and the subscriber line Ill is marked as idle to the connector switches having access thereto. Y

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modlncations as fall within the true spirit and scope of the invention.

v What is claimed is:

` r1. In a telephone system, first and second groups of lines, first and second finder switches, each of said finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto,` first blocking means normally eective positively to prevent said first finder switch from finding a line in said second group of lines, second blocking means normally effective positively to prevent said second finder switch from finding a line in said first group of lines, first start means operative'to initiate operation of said first finder switch. means for arresting operation of andfor rendering busy said first finder switch when a line is found thereby, means governed when said first flnder switch is rendered busy for rendering lneii'ective said second blocking means, second start means operative to initiate operation of said second nnder switch, means for arresting operation of and for rendering busy said second nder switch when'a line is found thereby, means governed when said second nder switch is rendered busy for rendering ineffective said first blocking means, and vmeans governed in response to the presence of a calling line in said first group of lines for operating said first start means in the event said first finder switch is -idle and for operating said second start means in the event said first finder switch is busy and governed in responseto the presence of a calling line in said second group of lines for operating'saidl second start means in the event said second finder switch is idle and for operating said first start :leans in the event said second finder switch is 2. In a telephone system, first and second groups of lines, rst and second finder switches, each of said finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, first blocking means operative to prevent said first finder switch from finding a/ line in said second group of lines, l second blockin'g means operative to 'prevent said second finder 'switch from finding a line in said first group of lines, first start means operative to initiate operation of said first finder switch, 'means for arresting operation of said first finder switch when a line is found thereby, second start means operative to initiate operation of said second finder switch, means for arresting operation of said second finder switch when a line is found thereby, means governed while both said first finder switch and said second finder switch are operating for operating both said first blocking means and said second blocking means, and means governed in response to the presence of a i calling line in said first group of lines for operating said first start means in the event said first nder switch is idle and for operating said second start means in the event said first finder switch is busy and governed. in response to the presence of a calling line in said second group of lines for operating said second start means in the event said second finderv switch is idle and for operating said first start means in the event said second f inder switch is busy.

3. In a telephone system, first and second groups of lines, first and second finder switches, each of said finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, first blocking means operative to prevent said rst finder switch from finding a line in said second group of lines, second blocking means operative to prevent said second finder switch from finding a line in said first group of lines, firststart means operative to initiate operation of said first finder switch, means for arresting operation of and for rendering busy said first finder switch when a line is found thereby, means governed while said first finder switch is operating and when said second finder switch is idle for operating said rst blocking means, second start means operative to initiate operation of said second finder switch, means for arresting operation of and for rendering busy said second finder switch when a line is found thereby, means governed while said second finder switch is operating and when said first finder switch is idle for operating said second blocking means, and means governed in response to the presence of a callingline in said first group of lines for operating said first start means in the event said first finder switch is idle and for operating said second start means in the event said rst finder switch is busy and governed in response to the presence of a calling line in said second group of lines for operating said second start means in the event said second finder switch is idle and for operating said first start means in the event said second finder switch is busy.

4. In a telephone system, first and second groups of lines, first and second finder switches, each of said finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto,riirst blocking means operative to prevent said iirst finder switch from finding a line in said second group of lines, second blocking means operative to prevent said second finder switch from finding aline in said first group of y lines, first start means operative to initiate operation of said first finder switch,l means for arresting operation of and for rendering busy said first finder switch when a line is found thereby, means governed while said first finder switch is operating and when said second finder switch is idle for operating said first blocking means, second start means operative to initiate operation of said second finder switch, means for arresting operation of and for rendering busy said second finder switch when a line is found'thereby, means governed while said second finder switch is operating and when said first finder switch is idle for operating said second blocking means, additional means governed while both said first finder switch and said second finder switch are operating for operating both said first blocking means and said second blocking means, and means governed in response to the presence of a calling line in said first group of lines foroperating said first start means in the event said first finder switch is idle and for operating said second start means in the event said first finder switch is busy and governed in response to the presence of a calling line in said second group of lines for operating said second start means in the event said second finder switch is idle and for operating said first start means in the event said second finder switch is busy. i

In a telephone system, first and second groups of lines, firstand second groups of finder l switches, each of the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, first blocking means normally effective positively to prevent the finder switches, in said first group of finder switches from finding lines in said second group of lines, second blocking means normally effective positively to prevent the finder switches in said second group of finder switches from finding lines in said first group lof lines, a first distributor operative to assign idle ones of the finder switches in said first group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, means governed when all of the finder switches in said first group of finder switches are rendered busy for rendering ineffective said second blocking means, a second distributor operative to assign idle ones of the finder switches in said second group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, ,means governed when all of the finder switches in said second group of` finder switches are rendered busy for rendering ineffective said first blocking means, and means governed in response to the presence of a calling line in said first group of lines for operating said first distributor in the event there is an idle finder switch in said first group of finder switches andfor operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second group of lines for switches, each of the finder switches in each of.

said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, flrst blocking means operative to prevent the finder switches in said first group of finder switches from fiindlng lines in said second groupof lines, second blocking means operative to prevent the finder switches in said second group of finder switches from finding lines in said first group of lines, a first distributor operative to assign idle ones of the finder switches in said first group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, a second distributor operative to assign idle ones of the finder switches inl said second group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arrestingl ioperation of and for rendering busy said last-mentioned finder switch when a line is found thereby, means governed when a finder switch in said first group of finder switches and a finder switch in said second group of finder switches are operating for operating both said first blocking means and said second blocking means, and means governed in response to the presence of a calling line in said first group of lines for operating said first distributor in the event there is an idle finder switch in said first group of finder switches and for operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second groupof lines for operating said second distributor in the event there is an idle finder switch in said second group of finder switches and for operating said first distributor in the event all of the finder switches in said second group of finder switches are busy.

7. In a telephone system, first and second groups of lines, first and second groups of finder switches, each of the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, first blocking means operative to prevent the finder switches in said rst group of finder switches from finding lines in said second .group of lines, second blocking means operative to prevent the finder switches in said second group of finder switches from finding lines in said first group of lines, a first distributor operative to assign idle ones of the finder switches in said first group of finder switches in a predetermined order and to initiate operation of an assigned one of said lastmentioned finder switches, means for arresting operation of and for rendering busy said lastmentioned finder switch when a line is found thereby, means governed while a finder switch in said first group of finder switches is operating 16 and when there is an idle finder switchl in said second group of finder switches for operating 'said first blocking means, a second distributor operative to assign idle ones of the finder vswitches in said second group oi' finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder 'switch when a line is found thereby, means governed while a finder switch in said second group of nder switches is operating and when there is an idle finder switch in said first group of finder switchesfor operating said second blocking means, and means governed in response to the presence of a calling line in said first group of lines` for operating said first distributor in the ev'ent there is an idle nden switch in said first group of nder switches and for operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second group of lines for operating said second distributor in the event there is an idle finder switch in said second group of finder switches and for operating said first distributor in the event all of the finder switches in'said second group of finder switches are busy.

8. In a telephone system, first and second groups of'lines, first and secondgroups of finder switches, eachkof the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operativeto find a calling line accessible thereto, first blocking means operative to prevent the finder switches in said first group of finder switches from finding lines in said second group of lines, second blocking means-operative to prevent the finder-switches in said second group of nder switches from finding lines in said first group of lines, a first distributor op,

erative to assign idle ones of the finder switches in said first group of finder switches in a predetermined order and to initiate operation of an assigned oneof said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, means governed while a finder switch in said first group of finder switches is operating and when there is an idle finder switch in said second group of finder switches for operating said first blocking means, a second distributor operative to assign idle ones of the finder switches in said second group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, means governed while a finder switch in said second group of finder switches is operating and when there isan idle finder switch in said first group of finder switches for operating said second blocking means, additional means governed while a finder switch in said first group of finder switches and a finder switch in said second group of finder switches are operating for operating both said first blocking means and said second blocking means, and means governed in response to the presence of a calling line in said first group of lines for operating said first distributor in the event there is an idle finder switch in said first group of finder switches and for operating said second distributor in the event all' of the finder switches in said first group of finder switches are busy and governed in response to the presence of ya calling line in said second group of lines for operating said second distributor in the event Vthere is an idle nder switch in said second group of finder switches and for operatingsaid first distributor in the event all of the finder switches in said second group of finder switches are busy.

9. In a telephone system, first and second groups of lines, first and second groups of finder switches, each of the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, first blocking means normally effective positively to prevent the finder switches in said first group of finder switches from finding lines in said second group of lines, second blocking means normally effective positively to prevent the finder switches in said second group of finder switches from finding lines in said first group of lines, a first distributor operative through a cycle to initiate operation of a preselected finder switch in said first group of -finder switches and then to arrest operation of and to render busy said last-mentioned finder switch when a line is found thereby and finally to select another idle onevof the finder switches in said first group of finder switches, means governed when all of the finder switches in said first group of finder switches are rendered busy for rendering ineffective said second blocking means, a second distributor operative through a cycle to initiate operation of a preselected finder switch in said second group of finder switches and then to arrest operation of and to render busy said last-mentioned finder switch when a line is found thereby and finally to select another idle one of the finder switches in said second group of finder switches, means governed when al1 ofv the finder switches in said second group of finder switches are rendered busy for rendering ineffective said first blocking means, and means governed in response to the presence of a calling line in said first group of lines for operating said first distributor in the event there is an idle finder switch in said first group of finder switches and for operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second group of lines for operating said second distributor in the event there is an idle finder switch in said second group of finder switches and for operating said first distributor in the event all of the finder switches in said second group of finder switches are busy.

10. In a telephone system, first and second groups of lines, first and second groups of finder switches, each of the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accesswitch when a line is found thereby and finally to select another idle one of the finder switches in said; first group offlnder switches, a second distributor operative through acycle to initiate operation of a preselected finder switch in said secondgroup of finder switches and then to arrest operation of and to render busy said lastmentioned iinder switch when a line is found.

thereby and finally to select another idle one of the findervswitches in said second group of finder switches,` means governed when a'flnder switch in said first group of finder switches and a finder switch in said second group of finder switches are operating for operating bothsaid first blocking i means and said Y second blocking means, and means governed in response-to the presence of a calling line in said first group of lines for operating said first distributor in the event there is an idle finder switchy in said first group of finder switches and for 'operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second group of lines for operating said second distributor in the event there is an idle finder switch in said second group of finder switches and for operating said first distributor ln'the event all of the finder switches in said second group of finder switches are busy.

11.` In a telephone system, first and second groups of lines, `first and second groups of finder switches, eachV of the nder switches in each of said groups of nder switches having access to each of the lines in each of said groups of lines` and being operative to nd a calling line acceser switch in said Vsecond group of finder switches and for operating said first distributor in the event all of the finder switches in said second group of finder switches are busy.

12.' In .a telephone system, first and second groups of lines, first and second groups of finder switches, each of the finder switchesineach of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative Vto nd a calling line accessible thereto, first blocking means operative 'to prevent the finder `switches in said first group 'of finder switchesfrom finding lines in said second group of lines, second blocking means operative to prevent the finder switches in said second group of finder switches from finding lines in said first group of lines, a first distributor operative through a cycle to initiate operation sible thereto,`rst blocking means 'operative to prevent the finder switches in said first group of finder switches `from finding lines in said second group of lines, second blocking means operative to prevent thevfinder switches in said second group of nder switches from finding lines in said first group of lines, a first distributor opera- -tive `through a' cycle to initiate operation of a preselected finder switch in said iirst group of finder switches and then to arrest operation of and to render busy said last-mentioned finder switch when a line is found thereby and finally to select another idle one of the finder switches in said first group of finder switches, means governed while a finder switch in said first group of l,

finder switches is operating and when there is an of a lpreselectedfinder switch in said first group of finder switches and then to arrest operation of and to render busy said last-'mentioned finder switch when a line is found thereby and finally to select another idle one -of the finderswitches in said first group of finder switches, means governed while a finder switch in said first group of finder switches is operating and when there is an idle finder switch in said second group of finder switches for operating said first blocking means, a second distributor operative through a cycle to initiate operationof la preselected nder switch `in said second group of finder switches -and then to arrest operation of and to render busy said last-mentioned finder switch when a .line is found thereby and finally to select another idle one ofthe finder switches in said second group of finder switches, means governed While a finder switch in said second group of finder switches is operating and when there is an idle finder switch in said first group of. finder switches for operating said second blocking means, additional means governed while a lnder idle iinder'switch in said second group of finder switches for` operating said first blocking means, a second distributor operativethrough a cycle to initiate operation of a preselected finder switch in said second group of finder switches and then f' to arrest operation of and to render busy said last-mentioned finder switch when a line is found finder switch in said first group of finder switches and for operating said second distributor in the event al1 of the finder switches in said first group of finder switches are busy and lgoverned in response to the presence of a calling line in `said second groupof lines for operating said second distributor in the event there is an idle findswitch in said first group of finder switches and a finder switch in `said second group of finder switches areoperating for operating both said first blocking means and said second blocking means, and means governed in response to the presence of la calling line in said first group of lines for operating said first distributor in the event there is an idle finder. switch in said first group of finder switches and for operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second group of lines for operating said second distributor in the event there is an idle finder switch in said second group of finder switches and for operating said first distributor in the event all of the finder switches in said second group of finder switches are busy.

13. In a telephone system, first and second groups of lines, first and second groups of finder switches, each of the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find `a calling line accessible thereto, a first blocking circuit adapted to be completed to prevent the finder switches in said first group of finder switches from finding lines in said second group of lines, a second4 blocking circuit adapted to be completed to prevent the finder switches in said second group of finder switches from finding lines in. said first group of lines, a first distributor operative toassign idle ones of the finder switches in said first group of finder switches in a predetermined order and to initiate operation of an assigned on'e of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, a second distributor operative to assign idle ones of the finder switches in said second group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches,

means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, means included in said first distributor and governed when a finder switch in saidrst group of rnder switches l is operating for preparing points in both said first blocking circuit and said second blocking circuit, means included in said second distributor and governed when a finder switch in said second group of finder switches is operating for preparing points in both said first blocking circuit and said second blocking circuit, each of said blocking circuits being completed only when points are prepared therein in both said first distributor and said second distributor, and means governed in response to the presence of a calling line in said first group of lines for operating said first distributor in the event there is an idle finder switch in said first group of finder switches and for operating said second distributor in the event all of the finder switches in said first group of nder switches are busy and governed in response to the presence of a calling line in said second group of lines for operating said second distributor in the event there is.. an idle finder switch in said second group of finder switches and for operating said first distributor in the event all of the finder switches in said second group of finder switches are busy. v y

14. In a telephone system, first and second groups of lines, first and second groups of finder switches, each of the nder switches in each of said groups of finder switches having access to each of the lines in each of said groups of' lines and being operative to find a calling line accessible thereto, a first blocking circuit adapted to be completed t prevent the finder switches in said first group of finder switches from nding lines in said second group "of lines, a second blocking circuit adapted to be completed to prevent the finder switches in said second group of finder switches from finding lines in said first y group of lines, a first distributor operative to assign idle ones of the finder switches in said first group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, a second distributor operative to assign idle ones of the finder switches in said second group of finder switches in a predetermined order and to initiate operation of an assigned one of said lastmentioned finder switches,l means for arresting operation of and for rendering busy said lastmentioned nder switch when a line is found thereby, means included in said first distributor and governed while a finder switch in said first group of nder switches is operating for preparing a point in said first blocking circuit, additional means included in said first distributor and governed when there is an idle finder switch in said first group of finder switches for preparing a point in said second blocking circuit, means included in said second distributor and governed while a finder switch in said second group of finder switches is operatingfor preparing a point in said second blocking circuit, additional means included in said second distributor and governed when there is an idle finder switch in said second group of finder switches for preparing a point in said first blocking circuit, each of said blocking circuits being completed only when points are prepared therein in both said first distributor and said second distributor, and means governed in response tothe presence of a calling line in said first group of lines .for operating said first distributor in the event there is an idle finder switch in said first group of finder switches and for operating said second distributor in the event all of the finder switches in said first group of finder switches are busy and governed in response to the presence of a calling line in said second group of lines for operating said second distributor in the event there is an idle finder switch in said second group of finder switches and for operating said first distributor in the event all of the finder switches in said second group of finder switches are busy.

l5. In a telephone system, first and second groups of lines, first and second groups of finder switches, each of the finder switches in each of said groups of finder switches having access to each of the lines in each of said groups of lines and being operative to find a calling line accessible thereto, a first blocking circuit adapted to be completed to prevent the finder switches in said first group of finder switches from finding lines in said second group of lines, a second blocking circuit adapted to be completed toprevent the finder switches in said second group of finder switches from finding lines in said first group of lines, a first distributor operative to assign idle ones of the finder switches in said first group of iinder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned nder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, a second distributor operative to assign idle ones of the finder switches in said second group of finder switches in a predetermined order and to initiate operation of an assigned one of said last-mentioned finder switches, means for arresting operation of and for rendering busy said last-mentioned finder switch when a line is found thereby, means included in said first distributor and governed While a finder switch in said first group of nder switches is operating for preparing a point in said first blocking circuit, additional means included in said first distributor and governed while a finder switch in said first group of nder switches is operating or when there is an idle finder switch in said first group of finder switches for preparing a point in said second blocking circuit means included in said second distributor and governed while a finder switch in said second group of finder switches is operating for preparing a point in said second blocking circuit, additional means included in said second distributor and governed while a finder switch in said second group of finder switches is operate ing or when there is an idle finder switch in said second group of nder switches for preparing a point in said first blocking circuit, each of said blocking circuits being completed only 

